Silicon-based rf system and method of manufacturing the same

ABSTRACT

A RF system which includes a silicon substrate formed with at least one via-hole filled with conductive material so that both sides of the silicon substrate are electrically connected with one another; at least one flat device formed on one side of the silicon substrate; and at least one RF MEMS device formed on the other side of the silicon substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Rule 53(b) Divisional Application of U.S.application Ser. No. 11/342,564 filed Jan. 31, 2006, which claimsbenefit of Korean Patent Application No. 2005-11901 filed Feb. 14, 2005in the Korean Intellectual Property Office. The above-noted applicationsare incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a RF system implemented on a singlesilicon-based chip and a method for manufacturing the same.

2. Description of the Related Art

With the recent rapid development of communication technologies, thereis a need for corresponding development of RF (Radio Frequency) devicetechnologies. In particular, due to multi-functionalization, there is ademand for miniaturization and integration of wireless communicationterminals such as mobile phones. For this reason, nowadays,micro-machining of electronic devices through MEMS (Micro ElectricalMechanical System) technologies is performed as practiced by those ofordinary skill in the art.

Individual electronic devices processed in this manner are integrated ona LTCC (Low Temperature Co-fired Ceramic) substrate or a MLB(Multi-Layer Board) substrate formed by laminating plural PCBs (PrintedCircuit Boards) to implement a RF system. The RF system implemented onsuch a LTCC substrate or MLB substrate forms a predetermined circuittherein through an inductor, a capacitor or the like implemented in atwo-dimensional structure, and various active devices such as a LNA (LowNoise Amplifier), PA (Power Amplifier), or the like and RF MEMS devicessuch as a filter, switch, duplexer or the like which arethree-dimensional devices are formed on top of the RF system.

The above-mentioned RF system is formed with a separate protective filmfor protecting the three-dimensional RF MEMS devices, in which no deviceis formed in the protective film. For this reason, there is a limit inintegrating and miniaturizing such a RF system.

In addition, there is a disadvantage in that the size of the RF systemis increased because various active devices and RF MEMS devices aretwo-dimensionally arranged on the top side of the LTCC substrate or MLBsubstrate.

Furthermore, the RF MEMS devices are formed through a silicon process,whereas the LTCC board is formed through a LTCC process in which ceramicand glass materials are mixed and fired. Therefore, in order toimplement a RF system on such a LTCC substrate, there is a demand toform RF MEMS devices through a silicon process, to form a LTCC substrateby performing a LTCC process, and then to bond the RF MEMS to the LTCCboard. Meanwhile, in order to implement a RF system on a MLB substrate,a MLB process is performed to form a MLB substrate, in which processplural PCBS, each of which is formed with a predetermined circuitpattern, are laminated and then drilled to form interlayer electricinterconnections. Then, RF devices formed through a silicon process arebonded to the MLB substrate. Because different kinds of processes arerequired to implement a RF system, the manufacturing processes of such aRF system are difficult to perform and the manufacturing costs thereofare increased.

For this reason, various research has recently been proposed toimplement such a RF system through the same kinds of processes such as asilicon process.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-mentioned problems, and an object of the present invention is toprovide a RF system which can be manufactured through the same kind ofprocess and a method for manufacturing the same.

Another object of the present invention is to provide a RF system whichis advantageous in miniaturization and a method of manufacturing thesame.

Yet another object of the present invention is to provide a RF systemwhich is easy to manufacture and makes it possible to lowermanufacturing costs.

In order to achieve the above-mentioned objects, the present inventionprovides a RF system comprising: at least one silicon substrate; andplural RF devices respectively formed on either side of the siliconsubstrate.

According to an embodiment of the present invention, the at least onesilicon substrate comprises one substrate (i.e., the substrate is solelya single substrate), and the plural RF devices comprise: one or moreflat devices formed on one side of the silicon substrate; and one ormore RF MEMS devices formed on the other side of the silicon substrateto be electrically connected with the flat devices.

The flat devices may include at least one active device and at least onepassive device, wherein the at least one active device includes at leastone of a PA and a LNA, and the at least one passive device includes atleast one of an inductor, a capacitor, a resistor, and an antenna. Inaddition, the silicon substrate is formed with at least one groove forelectric isolation from the RF MEMS devices and one or more via-holesfor electrically interconnecting the RF MEMS devices and the flatdevices.

According to another embodiment of the present invention, the one sideof the silicon substrate is formed with a groove and the flat devicesare formed in the groove.

According to another embodiment of the present invention, the at leastone silicon substrate comprises a first silicon substrate formed with agroove on one side thereof, a second silicon substrate bonded to the oneside of the first silicon substrate, and a third silicon substratehaving one side bonded to the other side of the first silicon substrateto be electrically connected with the first silicon substrate, whereinthe RF devices are formed in the groove. The RF devices may comprise:one or more first flat devices formed on the one side of the firstsilicon substrate; and one or more RF MEMS devices formed on the surfaceof the second silicon substrate facing the first silicon substrate; oneor more second flat devices formed on the other side of the firstsilicon substrate; and one or more third flat devices formed on theother side of the third silicon substrate.

In addition, the first and third silicon substrates are respectivelyformed with one or more via-holes filled with conductive material and aninsulation layer is interposed between the first and third siliconsubstrates. Meanwhile, each of the first to third flat devicespreferably includes at least one of a PA, a LNA, an inductor, acapacitor, a resistor and an antenna.

In order to achieve the above-mentioned objects, the present inventionalso provides a method of manufacturing a RF system which comprises: a)forming one or more flat devices on one side of a silicon substrate; b)electrically connecting first and second sides of the silicon substrate;and c) forming one or more RF MEMS devices on the second side of thesilicon substrate.

According to an embodiment of the present invention, the step a)comprises: patterning one or more flat devices on the first side of thesilicon substrate, and the step b) comprises: b-1) coating a sacrificiallayer on the first side of the silicon substrate to protect the flatdevices; b-2) forming at least one via-hole through the siliconsubstrate; and b-3) filling the at least one via-hole with conductivematerial. In addition, in the step b-3), the conductive material isfilled in the at least one via-hole by sputtering. The step c)comprises: forming at least one groove on the second side of the siliconsubstrate; forming at least one RF MEMS device atop of the groove; andremoving the sacrificial layer.

According to another embodiment of the present invention, the step a)comprises: forming a groove on the first side of the silicon substrate;and patterning the flat devices in the groove.

In order to achieve the above-mentioned objects, the present inventionalso provides a method of manufacturing a RF system which comprises: A)preparing first, second and third substrates; B) forming a groove on afirst side of the first silicon substrate and forming at least one firstflat device and at least one second flat device on a second side of thefirst silicon substrate to fabricate a first silicon substrate assembly;C) forming at least one RF MEMS device on a first side of the secondsilicon substrate to fabricate a second silicon substrate assembly; D)forming a third flat device on a first side of the third silicon tofabricate a third silicon substrate assembly; and E) bonding the first,second and third silicon substrate assemblies to each other so that theat least one RF MEMS device is positioned within the groove.

According to another embodiment of the present invention, the step B)comprises: B-1) etching a groove in a predetermined depth on the firstside of the first silicon substrate; B-2) forming the at least one firstflat device in the groove; B-3) forming the at least one second flatdevice on the second side of the first silicon substrate; B-4)electrically connecting first and second sides of the first siliconsubstrate with each other; and B-5) forming an insulation film on thesecond side of the first silicon substrate. In addition, the step B-4)comprises steps of: forming at least one first via-hole through thefirst silicon substrate; filling the at least one first via-hole withconductive material; and forming at least one solder ball atop of the atleast one first via-hole filled with the conductive material, and thestep D) comprises: forming at least one third flat device on the thirdsilicon substrate; forming at least one second via-hole through firstand second sides of the third silicon substrate; and filling the secondvia-hole with conductive material. The step E) may comprise: bonding thesecond silicon substrate assembly to one side of the first siliconsubstrate assembly; and E-2) bonding the third silicon substrateassembly to the second side of the first silicon substrate, wherein thesteps E-1) and E-2) may employ a metal fusion bonding method.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects and features of the present invention will be moreapparent from the description of certain embodiments of the presentinvention in reference to the accompanying drawings, in which:

FIGS. 1A to 1D are process views illustrating a method of manufacturinga RF system according to a first embodiment of the present invention;

FIGS. 2A to 2D are process views illustrating a method of manufacturinga RF system according to a second embodiment of the present invention;and

FIGS. 3A to 3D are process views illustrating a method of manufacturinga RF system according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, embodiments of the present invention are described indetail with reference to accompanying drawings. However, the presentinvention should not be construed as being limited thereto.

Referring to FIG. 1, a RF system according to a first embodiment of thepresent invention includes a silicon substrate 110 and one or more RFdevices respectively formed on either side of the silicon substrate 110.

The silicon substrate 110 is formed with two grooves 112 on one side ofthe silicon substrate for electric isolation of the silicon substratefrom the RF devices, and one or more via-holes 114 through the siliconsubstrate 110. The via-holes 114 are filed with conductive material 116.

The RF devices include two RF MEMS devices 158, wherein each RF MEMSdevice 158 has a three-dimensional structure because it is fabricated bybeing stacked with four flat devices 152. In the present embodiment, thenumbers of the flat devices 152 and the RF MEMS devices 158 are definedas four and two, respectively. However, the numbers can be increased orreduced according to the characteristics of the RF system.

The flat devices 152 include two active devices 154 formed on the bottomside of the silicon substrate 110, a first passive device 156 a forinterconnecting the two active devices 154 in such a way that a signalcan be communicated between the two active devices 154, and a secondpassive device 156 b for interconnecting the two RF MEMS devices 158 insuch a way that a signal can be communicated between the two RF MEMSdevices 158. Each of the active devices 154 may be a PA, a LNA, etc. andthe first and second passive devices 156 a, 156 b may be an inductor, acapacitor, an antenna, a resistor, a transmission line, etc.

The RF MEMS devices 158 are directly formed on one side of the siliconsubstrate 110 through a MEMS technology. More specifically, the MEMSdevices 158 are formed atop and on one side of the grooves 112 toelectrically isolate the RF MEMS devices 158 from the silicon substrate110. Although the grooves 112 are employed as electrical isolation meansin the present embodiment, various isolation means such as insulationfilm can be alternatively employed. In addition, because they areelectrically connected with the conductive material filled in thevia-holes 114, the RF MEMS devices 158 can be electrically connectedwith the active devices 154 formed on the other side of the siliconsubstrate 110. Then, the two RF MEMS devices 158 are electricallyinterconnected through the second passive device 156 b. The RF MEMSdevices 158 may comprise various filters, switches, duplexers, etc.

Because the RF devices are respectively formed on either side of thesilicon substrate, it is possible to increase the integration rate perunit area of the silicon substrate, thereby lowering manufacturingcosts.

Now, the method of manufacturing the RF system according to theabove-mentioned embodiment of the present invention is described.

Referring to FIG. 1A, to manufacture the RF system according to thepresent embodiment, the two active devices 154 and the first passivedevice 156 a for electrically interconnecting the two active devices 154are firstly formed on the other side of the prepared silicon substrate110. More specifically, the active devices 154 and the passive device156 a are formed by being sequentially patterned. Since the patterningcan be implemented through various well-known technologies such asphotolithography and etching, detailed description thereof is omitted.

Referring to FIG. 1B, a sacrificial layer 160 is formed on the otherside of the silicon substrate 110. This is to prevent the active devices154 and the first passive device 156 a formed on the other side of thesilicon substrate 110 from being damaged by coming into contact with asubstrate holder or the like when forming the RF MEMS devices 158 (seeFIG. 1D) on the one side of the silicon substrate. For the sacrificiallayer 160, it is possible to employ a photoresist or epoxy film, anitride film or an oxide film.

Referring to FIG. 1C, the silicon substrate 110 is turned over so as toform the corresponding devices on the one side of the silicon substrate110. Then, the one or more via-holes 114 are formed through the siliconsubstrate 110. The via-holes 114 can be formed through various etchingprocesses. Next, conductive material 116 can be filled in the via-holes114 by plating or sputtering. Then, the two grooves 112 for electricisolation are formed on the one side of the silicon substrate 110. Suchgrooves 112 are formed to have a predetermined size and shape through aphotolithographic process and an etching process

Referring to FIG. 1D, the second passive device 156 b is patterned andformed on the one side of the silicon substrate 110. Then, the two RFMEMS devices 158 are sequentially formed atop of the grooves 112 so thatthey can be respectively electrically connected with the second passivedevice 156 b. Meanwhile, it is possible to form a separate insulationfilm (not shown) on the surface, where the RF MEMS devices 158 aresupported. Then, the sacrificial layer 160 (see FIG. 1C) is removed bywet etching, thereby completing fabrication of the RF system. Meanwhile,it is possible to additionally form a cap or the like for protecting theRF MEMS devices 158.

Because the RF MEMS devices 158 are directly formed on the siliconsubstrate 110 on which a RF system will be directly formed, it ispossible to simplify a conventional complicated process in which it isnecessary to perform different types of processes. Such different typesof processes might include a semiconductor process for forming separateMEMS devices 158 and a process for locating the finished RF MEMS devices158 on a LTCC substrate or a MLB substrate for forming the RF system.That is, because the RF devices 150 are integrated on the siliconsubstrate 110, it is possible to manufacture a RF system through thesame types of processes.

Now, a RF system according to a second embodiment of the presentinvention and a method of manufacturing the same are described in detailwith reference to FIGS. 2A to 2D.

Referring to FIG. 2D, a RF system according to the second embodiment ofthe present invention is different from the first embodiment in that afirst groove 211 is formed on the other surface of the silicon substrate210 and active devices 254 and a first passive device 256 a, which areflat devices, are formed in the first groove 211. Because the firstgroove 211 is formed, this feature has an advantage in that it is notnecessary to form a sacrificial layer for protecting the devices formedon the other side of the silicon substrate 210 unlike the firstembodiment.

Referring to FIG. 2A, the method of manufacturing the RF systemaccording to the second embodiment of the present invention firstlyemploys a photolithographic process and an etching process to form thefirst groove 211 on the other side of the silicon substrate.

Referring to FIG. 2B, two active devices 254 and one passive device 256a are formed in the first groove with the same method as the firstembodiment.

Referring to FIG. 2C, the silicon substrate 210 is worked on to form thevia-holes 214 on the one side of the silicon substrate, and then thevia-holes 214 are filled with conductive material 216, like the firstembodiment of the present invention. At this time, because the activedevices 254 and the passive device 256 a are formed in the first grooveformed on the other side of the silicon substrate 210, the activedevices 254 and the first passive device 256 a are not damaged by asubstrate holder or the like even if the silicon substrate is worked on.

Referring to FIG. 2D, second grooves 212 are formed on the one side ofthe silicon substrate 210 for electric isolation and RF MEMS 258 and asecond passive device 256 b are respectively formed, like the firstembodiment of the present invention.

Because the first groove 211 is previously formed, the process forforming a sacrificial layer can be omitted, whereby the process forfabricating a RF system is simplified.

Now, a RF system according to a third embodiment of the presentinvention and a method of manufacturing the same are described indetail.

Referring to FIG. 3D, the RF system according to the third embodiment ofthe present invention includes a first silicon substrate assembly 300, asecond silicon substrate assembly 320 bonded to the bottom side of thefirst silicon substrate assembly 300, and a third silicon substrateassembly 340 bonded to the top side of the first silicon substrateassembly 300.

The first silicon substrate assembly 300 includes a first siliconsubstrate 302, one or more first flat devices 310 formed on one side ofthe first silicon substrate 302, one or more second flat devices 312formed on the other side of the first silicon substrate 302, and aninsulation film 314 for isolating the second flat devices 312 and thesecond silicon substrate assembly 320.

A groove 304 is formed on the one side of the first silicon substrate302 and the first flat devices 310 are formed in the groove 304. Then,one or more via-holes 306 are formed and filled with first conductivematerial 308 so as to electrically interconnect the top and bottom sidesof the first silicon substrate 302.

The first flat devices 310 comprise two passive devices, which may beany of an inductor, a capacitor, a resistor and a transmission line. Inaddition, the two passive devices can be electrically connected witheach other by a circuit pattern formed on the one side of the firstsilicon substrate 302 in a predetermined pattern. Furthermore, aninsulation film can be formed on the one side of the first silicon 302,so that the first passive devices and the first silicon substrate 302can be electrically insulated from each other.

The second flat devices 312 comprise two active devices, which may be aPA, a LNA, etc. The two active devices can be also electricallyconnected with each other through a circuit pattern formed on the otherside of the first silicon substrate 302, and an insulation film may beinterposed between the active devices and the first silicon substrate302.

The insulation film 314 can employ various insulation materials such asan oxide film, an epoxy film, a nitride film, etc. In addition, solderballs 316 are formed on the insulation film 314 to correspond to thefirst via-holes 306 filled with the first conductive material 308. Thesolder balls 316 are formed to contact the first conductive material308, so that the top side and the bottom side of the insulation film 314can be electrically connected with one another.

The second silicon assembly 320 includes a second silicon substrate 322and one or more RF MEMS devices 324 formed on the top side of the secondsilicon substrate 322.

An insulation film (not shown) can be formed on the top side of thesecond silicon substrate 322 to insulate the RF MEMS devices 324 and thesecond silicon substrate 322, and a circuit of a predetermined pattern(not shown) is formed on the insulation film so as to be electricallyconnected with the first silicon substrate 302.

A pair of the RF MEMS devices 324 are formed to be positioned within thegroove 304 formed on the one side of the first silicon substrate 302 andelectrically connected with one another via the passive device 326. Inthis manner, the RF MEMS devices 324 are positioned within the groove304 to serve as an existing package substrate for protecting the RF MEMSdevices 324. This arrangement allows for savings in manufacturing costbecause it is possible to omit a separate substrate for an existingpackage. Furthermore, it is further advantageous in miniaturization.Such RF MEMS devices 324 may comprise a filter, a switch and a duplexer.

The third substrate assembly includes a third silicon substrate 342 andone or more third flat devices 350 formed on the top side of the thirdsilicon substrate 342.

The third silicon substrate 342 is formed with one or more secondvia-holes 346 filled with second conductive material 348 which is incontact with the solder balls 316. Therefore, the first siliconsubstrate 302 and the second silicon substrate 322 are electricallyconnected with one another via a circuit pattern (not shown), and thefirst silicon substrate 302 and the third silicon substrate 342 areinterconnected with one another through the first via-holes 306, thesolder balls 316 and the second via-holes 346.

A pair of the third flat devices 350 are formed on the top side of thethird silicon substrate 342 and each electrically connected by anunillustrated circuit pattern. Each of the third flat devices 350 may bean antenna and a mixer which is an active device. However, it ispossible to variously modify and use the above-mentioned first andsecond flat devices 310, 312 as well as the third flat devices 350according to the characteristics and functions of a RF system, beyondthe above-mentioned applications.

Now, the RF system according to the third embodiment of the presentinvention and the method of manufacturing the same is described.

In the method of manufacturing the RF system, it is necessary to firstlyfabricate the first, second and third substrate assemblies 300, 320, 340as shown in FIGS. 3A to 3D. Such fabrication progresses after firstlypreparing the first, second and third silicon substrates 302, 322, 342by polishing each to a proper thickness.

Referring to FIG. 3A, in the first silicon substrate assembly 300, thefirst silicon substrate 302 is firstly formed with the groove 304 in theone side thereof using an etching process, etc. Then, the first flatdevices 310 are formed in the groove 304. The first flat devices 310 canbe formed using various semiconductor processes such as depositing apredetermined circuit pattern or the like depending on the type of thedevices. Next, the second flat devices 312 are formed on the other sideof the first silicon substrate 302. Then, the via-holes 306 are formedthrough the first silicon substrate 302 using an etching process or thelike, and the first conductive material 308 is filled in the firstvia-holes 306 by a process such as plating or sputtering. Then, thesolder balls 316 are formed to contact the first conductive material 308and the insulation film 314 is formed over the second flat devices 312including the solder balls 316. At this time, because the second flatdevices 312 are very thin, the insulation film 314 is formed in athickness which is substantially thin as compared to that shown in FIG.3A. Through this procedure, the first silicon substrate assembly 300 iscompleted.

Referring to FIG. 3B, in the second silicon substrate assembly 320, atleast one RF MEMS device 324 and the passive device 326 forinterconnecting the RF MEMS devices 324 are formed in the second siliconsubstrate 322. In this manner, because the RF MEMS devices 324 aredirectly formed in the second silicon substrate 322 as in the first andsecond embodiments described above, the same types of processes can beemployed, whereby the entire process of manufacturing a RF system can beeasily performed. The MEMS devices 324 can be formed using the sametypes of processes as those employed in the first and second embodimentsof the invention.

Referring to FIG. 3C, in the third silicon substrate assembly 340, thethird flat devices 350 are formed on the top side of the third siliconsubstrate 342. Then, one or more second via-holes 346 are formed throughthe third silicon substrate 342, and the second conductive material 348is filled in the second via-holes 346 by plating or sputtering. Throughthis process, the third silicon substrate assembly 340 is completed.

Once the first, second and third silicon substrate assemblies 300, 320,340 are completed as described above, the respective silicon substrateassemblies 300, 320, 340 are bonded to one another. At first, the oneside of the first silicon substrate assembly 300 is bonded to the oneside of the second silicon substrate assembly 320. At this time, the RFMEMS devices 324 will be positioned within the groove 304. Then, thethird silicon substrate assembly 340 is bonded to the sub-assembly ofthe first and second silicon substrate assemblies 300, 320. In thisevent, the first conductive material filled in the first via-holes 306,the solder balls 316 and the second conductive material 348 filled inthe second via-holes 346 will be electrically connected with oneanother. In the process of bonding the first, second and third siliconsubstrate assemblies 300, 320, 340, it is preferable to employ a metalfusion bonding method (e.g., metal fusion bonding of the siliconsubstrate assemblies plated at their contacting portions with a metalsuch as Au, Au/Sn alloy, etc.) which can be performed at a relativelylow temperature and thus can reduce damage to the devices, wherein themetal (i.e., the blended metallic zone interconnecting the respectiveassemblies) can be Au—Au, Au/Sn—Au/Sn, Au/Sn—Au, etc.

By three-dimensionally forming a RF system as described above, it ispossible to implement a more highly integrated RF system.

As disclosed above, according to the present invention, because a RFsystem can be manufactured solely with a silicon process, the entiremanufacturing process is simplified, whereby manufacturing cost can belowered.

In addition, because RF MEMS devices are directly formed on a siliconsubstrate, the number of steps included in manufacturing a RF system canbe reduced.

Furthermore, because devices are arranged on either side of a substrate,high density integration can be realized, which is advantageous inminiaturization of a RF system.

Meanwhile, because the first silicon substrate also serves as a packagesubstrate for protecting the RF MEMS devices, it is advantageous notonly in miniaturization but also in lowering manufacturing costincluding material costs.

Moreover, because the RF MEMS devices are arranged in athree-dimensional structure in which respective substrates are stacked,the present invention is highly advantageous in terms of integration.

Although several embodiments of the present invention have been shownand described in order to exemplify the principle of the presentinvention, the present invention is not limited to the above-describedspecific embodiments. It will be understood that various modificationsand changes can be made by one skilled in the art without departing fromthe spirit and scope of the invention as defined by the appended claims.Therefore, it shall be considered that such modifications, changes andequivalents thereof are included within the scope of the presentinvention.

1-16. (canceled)
 17. A method of manufacturing a RF system whichcomprises: a) forming one or more flat devices on a first side of asilicon substrate having first and second sides; b) electricallyconnecting both sides of the silicon substrate with one another; and c)forming one or more RF MEMS devices on the second side of the siliconsubstrate.
 18. The method as claimed in claim 17, wherein step a)comprises: patterning one or more flat devices on the first side of thesilicon substrate.
 19. The method as claimed in claim 18, wherein stepb) comprises: b-1) coating a sacrificial layer on the first side of thesilicon substrate to protect the flat devices; b-2) forming at least onevia-hole through the silicon substrate; and b-3) filling the via-holewith conductive material.
 20. The method as claimed in claim 19, whereinstep b-3) comprises filing the conductive material in the via-hole bysputtering.
 21. The method as claimed in claim 20, wherein step c)comprises: forming at least one groove on the second side of the siliconsubstrate; forming at least one RF MEMS device atop of the groove; andremoving the sacrificial layer.
 22. The method as claimed in claim 17,wherein step a) comprises: forming a groove on the first side of thesilicon substrate; and patterning the flat devices in the groove.
 23. Amethod of manufacturing a RF system, which comprises: A) preparingfirst, second and third substrates; B) forming a groove on a first sideof the first silicon substrate and forming at least one first flatdevices and at least one second flat device on a second side of thefirst silicon substrate to fabricate a first silicon substrate assembly;C) forming at least one RF MEMS device on a first side of the secondsilicon substrate to fabricate a second silicon substrate assembly; D)forming a third flat device on a first side of the third silicon tofabricate a third silicon substrate assembly; and E) bonding the first,second and third silicon substrate assemblies to each other so that theRF MEMS device is positioned within the groove.
 24. The method asclaimed in claim 23, wherein step B) comprises: B-1) etching the groovein a predetermined depth on the first side of the first siliconsubstrate; B-2) forming the at least one first flat device in thegroove; B-3) forming the at least one second flat device on the secondside of the first silicon substrate; B-4) electrically connecting bothsides of the first silicon substrate with one another; and B-5) formingan insulation film on the second side of the first silicon substrate.25. The method as claimed in claim 24, wherein step B-4) comprises:forming at least one first via-hole through the first silicon substrate;filling the first via-hole with conductive material; and forming atleast one solder ball atop of the at least one first via-hole filledwith the conductive material.
 26. The method as claimed in claim 25,wherein step D) comprises: forming at least one third flat device on thethird silicon substrate; forming at least one second via-hole throughboth sides of the third silicon substrate; and filling the secondvia-hole with conductive material.
 27. The method as claimed in claim26, wherein step E) comprises: E-1) bonding the second silicon substrateassembly to one side of the first silicon substrate assembly; and E-2)bonding the third silicon substrate assembly to the other side of thefirst silicon substrate.
 28. The method as claimed in claim 27, whereinbonding steps E-1) and E-2) comprise metal fusion bonding.
 29. Themethod as claimed in claim 28, wherein said metal fusion bondingincludes bonding of metals selected from the group consisting of Au—Au,Au/Sn—Au/Sn and Au/Sn—Au.